BRIEF ACCOUNTS OF REGIONAL GEOLOGY OF SHAANXI PROVINCE

Strata of various ages are developed in Shaanxi Province except the Upper Cretaceous.There are a total of 263 stratigraphical units in the whole province. In the North China area the Mesozoic-Cenozoic strata are the best developed, but the Silurian and Devonian are absent.In the Yangtze area the Paleozoic and Mesozoic are widespsead but the Silurian and Devonian are missing in most pasts of the area.In the Qinling area,the Paleozoic,Proterozoic and late Archean are all well developed. The magmatic activity took place frequently and rock types are very complex.There are 4 phases of volcanic rocks and 18 horizons,with basic and intermediate-acid volcanic rocks predominating.The volcanism was the most intense in the Proterozoic.Intrusive rocks involve 8 phases,of which basic- ultrabasic rocks are mainly distributed in southern Shaanxi.8 rock zones（areas） may be distinguished,with the Caledonian rocks predominating,Diorite is mostly of continental crust anatexis type.Most Yanshanian rocks are represented by small-sized porphyry bodies.Granite is widespread,with the Mesozoic activity being the most intense.It inclndes 6 genetic types. Metamorphic rocks are also very widespread.8 metamorphic phases and 17 metamorphic units may be distinguished.The types of regional metamorphic facies are complete.Progressive metamorphism is nmon.In the Nortb.China area,middle Proterozoic to early Paleozoic covers exhibit low-grade metamor- phism and the features of metamorphism with a“multi-layered structure”. In the Yangtze area,no metamorphism has happened since the Sinian and the metamorphism belongs to the type of basement metamorphism with a“single- layered structure”.In the Qining area,strata had all undergone metamorpbism before the Permian,and the metamorphic rocks straw zonal distribution,and superimposed metamorphism. 3 Ⅰ-order,12 Ⅱ-order and 21 Ⅲ-order rectonto areas may be distinguished in the whole province,8 deep faults,13 major faults and 6 hiddfn faults have been recognized.The Qinling area is a graben-type geosyncline（aulacogen）, with the eugeosynclire occurrring in company with the migeosyncline.The North Dabs Mountains area is a semi-eugeosyncline,showing distinct features of tectonic migration.In the northern Shaanxi area the tiling upiift occurred frequently,the rivers were captured,and peneplain levels and terraces are well developed. The geological developement of the entire region has a history of about 3000 Ma,including the pre-Changchengian-Qingbaikouian,Sinian,Cambrian-Si- lurian,Devonian-Triassic and Jurassic-Quaternary stages.Among other things, the three important geological events are the Zhon gtiao movement,the Jinning movement and the Indosinian movement.